A fleur de cœur is a beautiful and poetic French idiom that literally translates to "at the flower of the heart" or "at the heart's surface". It's not a common, everyday phrase, making it quite unique to this song.
In the context of the song, it conveys a profound sense of overflowing emotion, where love is so intense it's palpable and close to the surface, almost bursting forth. Aznavour uses it to express a love that is deeply felt and constantly present, even amidst anxieties and unspoken feelings.
"Amour à fleur de cœur" is Charles Aznavour's quiet portrait of watching someone he loves while they sleep. He wakes early just to study their face in the pale morning light, moved by how innocent and unconsciously alluring they look at rest, caught between poses that are almost too tender and almost too intimate.
That tenderness carries a bittersweet weight. His heart is "à fleur de cœur," love sitting right at the surface, ready to spill over, but it also aches. He wants to wake the sleeper and share what he's feeling, yet holds back so the joy doesn't tip into a pain only he can name. The recurring chorus keeps returning to that same mix: joy pierced by anguish, a peaceful, dreaming lover who is both a comfort and a private torment.
By the end, Aznavour simply accepts it. Loving someone this deeply means carrying both sides at once: the sweetness of watching them sleep, and the ache of a love that can never fully be spoken.